Manipulating snow cover in an alpine bog: effects on ecosystem respiration and nutrient content in soil and microbes

Snow amount is expected to decline in the Northern hemisphere as an effect of climate warming. However, snow amount in alpine regions will probably undergo stronger interannual fluctuations than elsewhere. We set up a short-term (1 year) experiment in which we manipulated snow cover in an alpine bog, with the following protocol: snow removal at the end of winter; snow removal in spring; snow addition in spring; removal of all aboveground plant tissues with no snow manipulation; no manipulation at all. We measured, at different dates from late spring to early autumn: ecosystem respiration (ER), and concentrations of carbon (C), nitrogen (N) and phosphorus (P) in the soil and in microbes. We hypothesized that longer duration of snow cover will lead to: i) higher ER rates associated with increased microbial biomass; and ii) decreased soil nutrient availability. Contrary to our first hypothesis, ER and microbial C content were unaffected by the snow cover manipulations, probably because ER was decoupled from microbial biomass especially in summer, when CO2 efflux was dominated by autotrophic respiration. Our second hypothesis also was partially contradicted because nutrient content in the soil and in plants did not vary in relation to snow cover. However, we observed unexpected effects of snow cover manipulations on the N : P ratio in the microbial biomass, which declined after increasing snow cover. This probably depended on stimulation of microbial activity, which enhanced absorption of P, rather than N, by microbes. This may eventually reduce P availability for plant uptake.